Xanthonema P.C.Silva, 1979

Holotype species: Xanthonema exile (Klebs) P.C.Silva

Original publication and holotype designation: Silva, P.C. (1979). Review of the taxonomic history and nomenclature of the yellow-green algae. Archiv für Protistenkunde 121: 20-63.

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Description: Organism multicellular, forming uniseriate, unbranched filaments. Filaments free-living or forming pale to bright green aggregations as flakes, small surface coatings or wicks. Thalli generally straight but can be slightly curved or undulated. Some species fragile and filaments break apart into fragments, possibly even to single cells. Cells cylindrical or with slight median bulge or sometimes slightly curved. Cell wall delicate to robust, comprised of a single piece but segmented into two, often unequal parts just prior to cell division; H pieces absent. Chloroplasts one to very numerous; when single or in twos cupuliform or trough-shaped; when numerous, discoid. Chloroplasts always parietal and without pyrenoids. Reserve products typical of Tribophyceae. Dimensions: filament up to several cm long; cell length 4-70 _m; cell width 1.5-18 _m. Asexual reproduction by zoospores. Zoospores formed singly or in twos, fours, eights or more in each mother cell. Zoospores ovoid to strongly amoeboid, with one to many chloroplasts and generally two flagella [X. sessile (Vinatzer) Ran with single flagellum]. Zoospores swim for short period, become globular to elliptic and germinate into a new filament without attaching. Aplanospores and akinetes reported. Xanthonema develops preferentially on humid soils and especially in stagnant, slightly acidic water. One species is known from brackish water (X. fluviatile sp. nov). Genus especially reported from Europe, North Africa (Morocco), Argentina and Antarctica. Species distinctions based on the number and the dimension of chloroplasts, length and fragility of the filament, and on cell size and morphology. Xanthonema was proposed by Silva (1979) to replace Heterothrix, created in 1932a by Pascher for Bumilleria exilis Klebs. Heterothrix had been used previously by J. Mƒller (in Martius 1860) for a member of the Apocynaceae (for additional information, see Silva, 1979). Eighteen species of Heterothrix were listed by Ettl (1978a), and four new ones were subsequently described

Information contributed by: A. Couté. The most recent alteration to this page was made on 2021-10-07 by M.D. Guiry.

Taxonomic status: This name is of an entity that is currently accepted taxonomically.

Gender: This genus name is currently treated as neuter.

Most recent taxonomic treatment adopted: Kawai, H. & Nakayama, T. (2015). Introduction (Heterokontobionta p.p.), Cryptophyta, Dinophyta, Haptophyta, Heterokontophyta (except Coscinodiscophyceae, Mediophyceae, Fragilariophyceae, Bacillariophyceae, Phaeophyceae, Eustigmatophyceae), Chlorarachniophyta, Euglenophyta. In: Syllabus of plant families. Adolf Engler's Syllabus der Pflanzenfamilien. Ed. 13. Phototrophic eukaryotic Algae. Glaucocystophyta, Cryptophyta, Dinophyta/Dinozoa, Haptophyta, Heterokontophyta/Ochrophyta, Chlorarachnniophyta/Cercozoa, Chlorophyta, Streptophyta p.p. (Frey, W. Eds), pp. 11-64, 103-139. Stuttgart: Borntraeger Science Publishers.

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Contributors
Some of the descriptions included in AlgaeBase were originally from the unpublished Encyclopedia of Algal Genera, organised in the 1990s by Dr Bruce Parker on behalf of the Phycological Society of America (PSA) and intended to be published in CD format. These AlgaeBase descriptions are now being continually updated, and each current contributor is identified above. The PSA and AlgaeBase warmly acknowledge the generosity of all past and present contributors and particularly the work of Dr Parker.

Descriptions of chrysophyte genera were subsequently published in J. Kristiansen & H.R. Preisig (eds.). 2001. Encyclopedia of Chrysophyte Genera. Bibliotheca Phycologica 110: 1-260.

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Citing AlgaeBase
Cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 07 October 2021. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 28 March 2024

 
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